The invention is directed to ethylene-based polymer compositions that have improved extrusion coating, adhesion, and barrier properties. Polymer compositions based on LDPE are often used in extrusion coating applications. LDPE prepared using tubular technology (“tubular LDPE”) is more economical than LDPE prepared using autoclave technology (“autoclave LDPE”). However, “tubular LDPE” has lower melt strength, which often can lead to poorer extrusion coating properties. Thus, there is a need for new polymer compositions based on more economical “tubular LDPE,” and which have improved extrusion coating properties. There is a further need for such compositions that have improved adhesion and barrier properties.
International Publication WO 2014/081458 discloses compositions comprising a first ethylene-based polymer, formed by a high pressure, free-radical polymerization process, and comprising the following properties: a) a Mw(abs) versus melt index I2 relationship: Mw(abs)<A×[(I2)B], where A=5.00×102 (kg/mole)/(dg/min)B, and B=−0.40; and b) a MS versus I2 relationship: MS≥C×[(I2)D], where C=13.5 cN/(dg/min)D, and D=−0.55. These compositions can be used to form coatings, film, foam, laminate, fibers, tapes, wire and cable, and woven or non-woven fabrics.
B. H. Gregory, Extrusion Coating, A Process Manual, 2010, page 141, discloses HDPE/LDPE blends for extrusion coating. International Publication WO 2005/068548 discloses a polymer composition for extrusion coating with good process properties comprising a multimodal high density polyethylene and a low density polyethylene.
International Publication WO 2013/078018 discloses compositions comprising an ethylene-based polymer comprising the following properties: a) a melt index (I2)>2.0 dg/min; b) a Mw(abs) versus I2 relationship: Mw(abs)<A+B(I2), where A=2.40×105 kg/mole, and B=−8.00×103 (g/mole)/(dg/min); and c) a G′ versus I2 relationship: G′>C+D(I2), where C=127.5 Pa, and D=−1.25 Pa/(dg/min). The invention also provides an ethylene-based polymer comprising the following properties: a) a melt index (I2)>2.0 dg/min; b) a G′ versus I2 relationship: G′>C+D(I2), where C=127.5 Pa, and D=−1.25 Pa/(dg/min) c) a chloroform extractable (Clext) versus G′ relationship: Clext.<E+FG′, where E=0.20 wt %, and F=0.060 wt %/Pa; and d) a “weight fraction (w) of molecular weight greater than 106 g/mole, based on the total weight of polymer, and as determined by GPC(abs), “that meets the following relationship: w<I+J(I2), where I=0.080, and J=−4.00×10−3 min/dg. The compositions can be used for extrusion coating applications.
U.S. Pat. No. 7,956,129 discloses polymer blends comprising (a) 1-99% by weight of a copolymer of ethylene and an alpha olefin having from 3 to 10 carbon atoms, said copolymer having (iv) a density in the range 0.905 to 0.940 g·cm−3, (v) a melt elastic modulus G′ (G″=500 Pa) in the range 10 to 150 Pa, and (vi) a melt index in the range 5 to 50, and (b) from 1-99% by weight of a low density polyethylene (LDPE) polymer having a density from 0.914 to 0.928 g·cm−3, wherein the sum of (a) and (b) is 100%. The copolymers of component (a) are typically prepared by use of metallocene catalysts. The blends exhibit advantageous melt elastic modulus in the range 30 to 200 Pa. The blends are disclosed as suitable for extrusion coating applications.
International Publication WO 2014/081458 discloses an extrusion coating process of a polyethylene resin on a substrate, and where the polyethylene resin has a density from 0.940 g/cm3 to 0.960 g/cm3, and is prepared in the presence of an activated bridged bis-(tetrahydro-indenyl) metallocene catalyst. The resin may be used alone or in combination with LDPE.
U.S. Pat. No. 7,812,094 discloses a polymer blend suitable for the production of film, said polymer blend comprising at least (1) a multimodal high density polyethylene (HDPE) composition, and (2) a low density polyethylene (LDPE) polymer, a linear low density polyethylene (LLDPE) polymer or a mixture of LDPE and LLDPE polymers. The HDPE composition comprising a multimodal HDPE polymer, which contains at least a lower molecular weight (LMW) polyethylene component and a higher molecular weight (HMW) polyethylene component.
Other ethylene-based polymer compositions for coatings and/or other applications are disclosed in the following references: U.S. Pat. Nos. 8,247,065, 6,291,590, 7,776,987; International Publications Nos. WO83/00490, WO2015/092662, WO 2014/190041, WO 2014/190036, WO 2014/190039, WO2013178242A1, WO2013178241A1, WO 2013/078224; European Patent Application Nos. 1187876A1, EP0792318A1, EP1777238A1, EP2123707A1, and EP2123707A1. See also, A. Ghijsels et al., Melt Strength Behavior of Polyethylene Blends, Intern. Polymer Processing, VII, 1992, pp. 44-50; M. Xanthos et al., Measurement of Melt Viscoelastic Properties of Polyethylenes and Their Blends—A Comparison of Experimental Techniques, Polymer Engineering and Science, Vol. 37, No. 6, 1997, pp. 1102-1112; INEOS, Olefins and Polymers Europe, Your Partner in Extrusion Coating, Goods that Make Our Life Convenient, prior to May 2015, six pages; K. R. Frey, Polyethylene and Polypropylene in Flexible Barrier Packaging, 2009 Consumer Packaging Solutions for Barrier Performance course, TAPPI Place, 45 pages; N. Savargaonkar et al., Formulating LLDPE/LDPE Blends for Abuse—Resistant Blown Film, Plastics Technology, 2014, pp. 44-47 and 50.
However, as discussed above, there is a need for new polymer compositions, based on more economical “tubular LDPE,” and which have improved extrusion coating properties. There is a further need for such compositions that have improved adhesion (for example, Heat Seal Strength) and barrier (for example, Water Vapor Transmission Rate) properties. These needs have been met by the following invention.